1. Field of the Invention
The present invention relates to a reflection type display device which performs display by using external light such as natural light, and more specifically, it relates to an illumination structure of a reflection type display device used as an auxiliary when external light is scarce.
2. Description of the Related Art
A display device using an electro-optical material such as a liquid crystal is shaped like a flat panel and is characterized by its thinness, light weight, and low consumption of electric power. By using such characteristics, a liquid crystal display device is used for a display of a portable information apparatus or the like. Differing from an emissive device such as an LED, a liquid crystal display device (LCD) performs display by transmitting and shutting out external light in response to a voltage. Therefore, the liquid crystal display device requires an illumination structure, which is generally classified into two types, i.e., a transmission type using a backlight and a reflection type using natural light.
In a display device of the transmission type, a panel in which a liquid crystal as an electro-optical material is held between a pair of transparent substrates is fabricated, and a light source (backlight) for illumination is placed on the rear of the panel. The image is viewed from the front of the panel. A backlight is essential to the device of the transmission type, and, for example, a cold cathode fluorescent tube is used. From the viewpoint of the display device as a whole, the backlight consumes most of the electric power, which is unsuitable for displays of portable information apparatuses. On the contrary, in a display device of the reflection type, a reflector is placed on the rear of the panel, and external light such as natural light enters from the front. The image is viewed also from the front of the panel by making use of the reflected light. In contrast to the transmission type, the reflective type does not use a light source for supplying illumination light in the back, and thus the reflection type consumes relatively low electric power, which is suitable for displays of portable apparatuses. However, in the reflection type display device, the image cannot be viewed in an environment where external light is scarce, for example, at night, which remains a problem to be solved.